Nanoscale Copper–Tin Dioxide Interfaces for Efficient CO ₂ Electroreduction to Formic Acid and Formate at High Rates

This study reports highly selective and stable electrocatalysts consisting of Cu and Sn for efficient reduction of CO₂ to formate (HCOO^-) and formic acid (HCOOH). The copper-tin dioxide catalyst (CuSn) is prepared through a one-pot microwave-assisted solvothermal method. Different samples are obtained by varying Cu-to-Sn atomic ratios from 4 to 1. When Sn content is low, the CuSn sample shows a main crystalline phase of cuprous oxide (Cu₂O), with low amounts of surface CuO and SnO₂ species. An increase in Sn percentage leads to the appearance of the crystalline phase of metallic Cu and SnO₂, which becomes dominant for the sample with the highest Sn content. During CO₂ electrolysis, the optimal CuSn material shows a faradaic efficiency (FE) for HCOO^- greater than 90% at -200 mA cm^-2 in a flow cell with alkaline electrolyte. It also performs well under acidic condition (pH 3) to produce HCOOH with an FE of 70% at the same current density. A long-term test is carried out in 1 M KOH at -100 mA cm^-2 for over 20 h, showing good retention in FE_HCOO-. This study highlights the potential of implementing low-cost catalysts for CO₂ conversion at an industrial scale.